Flow battery cycle recovery system and method

Abstract

A flow battery cycle recovery system and method. The flow battery cycle recovery system comprises: a positive electrode liquid storage tank containing a positive electrode electrolyte, wherein the positive electrode electrolyte contains reducing ions and active ions, and the reducing ions can react with the active ions to reduce the valence state of the active ions and generate a first oxidizing gas; a catalytic reaction apparatus containing a catalyst, wherein the catalytic reaction apparatus can receive the first oxidizing gas to oxidize and immobilize the catalyst; and a negative electrode liquid storage tank containing a negative electrode electrolyte, wherein the negative electrode electrolyte undergoes a side reaction to generate a first reducing gas. The catalytic reaction apparatus can receive the first reducing gas, the first reducing gas is used for reducing the oxidized catalyst, and the resulting acid gas can be returned to the negative electrode liquid storage tank.

Description

A flow battery cycle recovery system and recovery method

[0001] This application claims priority to Chinese Patent Application No. 202411438680.5, filed on October 15, 2024, entitled "A Flow Battery Cyclic Recovery System and Recovery Method", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of flow battery technology, specifically to a flow battery cycle recovery system and recovery method. Background Technology

[0003] During long-term charge and discharge of a flow battery, the hydrogen evolution side reaction at the negative electrode causes the average valence state of the positive and negative electrode solutions to gradually increase, which in turn leads to a decrease in the capacity of the flow battery. In order to restore the capacity of the flow battery, a reducing agent is usually added to the positive electrode solution under high state of charge (SOC) conditions. High-valence active ions with strong oxidizing properties can undergo redox reactions with the reducing agent to generate low-valence active ions, thereby reducing the average valence state of active ions in the positive and negative electrode electrolytes.

[0004] Fuel cells can also be constructed using reducing gases and positive electrode solutions, such as hydrogen, and noble metal catalysts can be used to catalytically reduce the positive electrode active material and lower its valence state.

[0005] Neither of the above methods is a good choice for flow battery recovery.

[0006] Invention Overview

[0007] In a first aspect, embodiments of this application disclose a flow battery cycle recovery system, which includes:

[0008] A positive electrode storage tank is provided, which contains a positive electrode electrolyte containing reducing ions and active ions. The reducing ions can react with the active ions to reduce the valence state of the active ions and generate a first oxidizing gas.

[0009] A catalytic reaction device, wherein the catalytic reaction device contains a catalyst, the catalytic reaction device is connected to the positive electrode storage tank, the catalytic reaction device is capable of receiving the first oxidizing gas, and the first oxidizing gas is used to oxidize and fix the catalyst;

[0010] A negative electrode storage tank is provided, which contains a negative electrode electrolyte. The negative electrode electrolyte contains a supporting electrolyte, which is prone to undergoing a side reaction during battery charging or in the charging state to generate a first reducing gas. The negative electrode storage tank is connected to the catalytic reaction device, which can also receive the first reducing gas. The first reducing gas is used to reduce the oxidized catalyst. The generated acidic gas can be returned to the negative electrode storage tank and absorbed by the negative electrode electrolyte.

[0011] Secondly, embodiments of this application also provide a method for the cycle recovery of a flow battery, comprising the following steps:

[0012] The positive electrode storage tank contains a positive electrode electrolyte containing reducing ions and active ions. The reducing ions react with the active ions to reduce the valence state of the active ions and generate a first oxidizing gas.

[0013] The first oxidizing gas is introduced into a catalytic reaction device containing a catalyst. The first oxidizing gas reacts with the catalyst to oxidize and fix the catalyst.

[0014] The negative electrode storage tank contains a negative electrode electrolyte, which contains a supporting electrolyte. The supporting electrolyte is prone to side reactions during battery charging or in the charging state to produce a first reducing gas.

[0015] The first reducing gas is introduced into the catalytic reaction device, where it undergoes an oxidation-reduction reaction with the oxidized catalyst. The catalyst is reduced and releases acidic gas, which is then returned to the negative electrode storage tank and absorbed by the negative electrode electrolyte.

[0016] Compared with the prior art, the flow battery cycle recovery system of this application includes: a positive electrode storage tank containing a positive electrode electrolyte containing reducing ions and active ions, wherein the reducing ions can react with the active ions to reduce the valence state of the active ions and generate a first oxidizing gas; a catalytic reaction device containing a catalyst connected to the positive electrode storage tank, which can receive the first oxidizing gas and is used to oxidize the catalyst; and a negative electrode storage tank containing a negative electrode electrolyte containing a supporting electrolyte, which is prone to side reactions during battery charging or in a certain state to generate a first reducing gas; the negative electrode storage tank is connected to the catalytic reaction device, which can also receive the first reducing gas and is used to reduce the oxidized catalyst. The flow battery cycle recovery system of this application maintains the valence state balance of the positive and negative electrode solutions without adding a recovery agent to the positive electrode solution, reducing electrolyte contamination and enabling the application of long-life, non-degradation flow batteries. This application relates to a flow battery cycle recovery system, which also introduces an auxiliary reducing gas source to achieve full reduction of the catalyst and enable the catalyst to be recycled.

[0017] An embodiment of this application provides a method for the cycle recovery of a flow battery, comprising the following steps: A positive electrode electrolyte is contained in a positive electrode storage tank. The positive electrode electrolyte contains reducing ions and active ions. The reducing ions react with the active ions to reduce the valence state of the active ions and generate a first oxidizing gas. The first oxidizing gas is introduced into a catalytic reaction device containing a catalyst. The first oxidizing gas reacts with the catalyst to oxidize the catalyst. A negative electrode electrolyte is contained in a negative electrode storage tank. The negative electrode electrolyte contains a supporting electrolyte. The supporting electrolyte is prone to side reactions during battery charging or in a certain state, generating a first reducing gas. The first reducing gas is introduced into the catalytic reaction device. The first reducing gas reacts with the oxidized catalyst to undergo a redox reaction. The catalyst is reduced and releases an acidic gas. The generated acidic gas can return to the negative electrode storage tank and be absorbed by the negative electrode electrolyte. The method of this application links the recovery process with the capacity decay and SOC of the flow battery, realizing the automatic operation of flow battery recovery; and the method of this application can also be configured with an optional external reducing gas source recovery system, which can make external intervention adjustments to the electrolyte according to the actual operating conditions. Attached Figure Description

[0018] The technical solution and other beneficial effects of this application will become apparent from the following detailed description of specific embodiments in conjunction with the accompanying drawings.

[0019] Figure 1 is a connection diagram of the flow battery cycle recovery system provided in an embodiment of this application;

[0020] Figure 2 is a connection diagram of the positive electrode recovery device provided in an embodiment of this application;

[0021] Figure 3 is a schematic diagram of the connection of the reducing gas source provided in an embodiment of this application;

[0022] Figure 4 is a schematic diagram of the flow battery structure;

[0023] Figure 5 is a flowchart of the flow battery cycle recovery method provided in the embodiment of this application;

[0024] Figure 6 is a comparison diagram of the catalyst provided in the embodiments of this application before and after chlorine oxidation and before and after hydrogen reduction;

[0025] Explanation of reference numerals in the attached diagram: 10-Positive electrode storage tank, 101-First gas outlet, 102-First gas inlet, 103-First liquid outlet, 104-First liquid inlet, 20-Catalytic reaction device, 201-Second gas inlet, 202-Second gas outlet, 30-Negative electrode storage tank, 301-Fourth gas outlet, 302-Fourth gas inlet, 40-First pipeline, 401-First one-way valve, 50-Second pipeline, 60-Positive electrode Recovery device, 601-Second liquid inlet, 602-Second liquid outlet, 603-Third gas outlet, 604-Third gas inlet, 70-Third pipeline, 80-Fourth pipeline, 90-Fifth pipeline, 901-Second one-way valve, 100-Sixth pipeline, 200-Seventh pipeline, 2001-Third one-way valve, 300-Eighth pipeline, 400-Reduction gas source, 500-Tail gas treatment device. Detailed Implementation

[0026] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0027] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection, an electrical connection, or a connection that allows for mutual communication; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two elements or the interaction between two elements. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances. In the description of this application, "multiple" means two or more, unless otherwise expressly and specifically limited. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more features.

[0028] In the embodiments of this application, the reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0029] The following disclosure provides many different implementations or examples for carrying out different structures of this application. To simplify the disclosure of this application, the components and arrangements of specific examples are described below. Of course, these are merely examples and are not intended to limit this application.

[0030] As an introduction to the embodiments of this application, the flow battery is an electrochemical energy storage technology proposed by Thaler, and is a new type of battery. A flow battery consists of a stack unit, electrolyte, electrolyte storage and supply unit, and management and control unit. It is a high-performance battery that utilizes separate positive and negative electrolytes for independent circulation, featuring high capacity, wide application range (environment), and long cycle life. As a novel large-scale, high-efficiency electrochemical energy storage technology, flow battery technology achieves the interconversion and storage of electrical and chemical energy through the valence state changes of reactive substances. A schematic diagram of the flow battery structure is shown in Figure 4. The positive and negative electrolytes are stored in two separate tanks, and a pump is used to circulate the electrolyte within the battery system. Inside the battery stack, the positive and negative electrolytes are separated by an ion exchange membrane (or ion separator), and the battery is connected to an external load and power source. During the charging and discharging process, the positive and negative electrolytes undergo redox reactions on the electrodes inside the battery stack. With continuous charge and discharge cycles, the charge and discharge capacity of the flow battery will inevitably decrease to varying degrees.

[0031] Taking vanadium-containing flow batteries as an example, the increase in the average valence state of vanadium ions in the electrolytes of both the positive and negative electrodes due to the hydrogen evolution reaction at the negative electrode is one of the important reasons for the capacity decay of flow batteries. (Positive electrode VO2) + / VO2+ negative electrode V 3+ / V 2+ Initially, the masses of the positive and negative electrode active materials are equal. During cycling, the negative electrode electrolyte continuously undergoes a hydrogen evolution reaction: 2V 2+ +2H + =2V 3+ +H2↑;

[0032] This causes the valence state of vanadium ions to continuously increase, which manifests as a gradual increase in the concentration of pentavalent vanadium in the positive electrode solution at the end of the discharge step, directly leading to a gradual decrease in battery capacity.

[0033] To restore battery capacity, reducing agents are typically added to the positive electrode solution under high state of charge (SOC) conditions. High-valence active ions with strong oxidizing properties can react with these reducing agents in a redox reaction to generate low-valence active ions, thereby lowering the average valence state of the active ions in both the positive and negative electrode electrolytes. However, this method continuously introduces redox reaction residues from the reducing agent. On the other hand, fuel cells are another current research and application direction. They use reducing gases and positive electrode solutions to construct the battery, employing noble metal catalysts to catalyze the reduction of the positive electrode active material and lower its valence state. However, because noble metal catalysts are prone to detaching into the electrolyte, this exacerbates hydrogen evolution at the negative electrode, leading to a rapid decline in battery capacity.

[0034] Therefore, there is an urgent need for a method to restore the capacity of flow batteries without introducing chemical substances to contaminate the electrolyte.

[0035] Based on the above problems, referring to Figure 1, this application provides a flow battery cycle recovery system, including: a positive electrode storage tank 10, a catalytic reaction device 20, and a negative electrode storage tank 30. The positive electrode storage tank 10 contains a positive electrode electrolyte containing reducing ions and active ions. The reducing ions can react with the active ions to reduce the valence state of the active ions and generate a first oxidizing gas. The catalytic reaction device 20 contains a catalyst and is connected to the positive electrode storage tank 10. The catalytic reaction device 20 can receive the first oxidizing gas, which is used to oxidize the catalyst. The negative electrode storage tank 30 contains a negative electrode electrolyte containing a supporting electrolyte. The supporting electrolyte is prone to side reactions during battery charging or in a certain state to generate a first reducing gas. The negative electrode storage tank 30 is connected to the catalytic reaction device 20, which can also receive the first reducing gas. The first reducing gas is used to reduce the oxidized catalyst, so that the generated acidic gas can return to the negative electrode storage tank 30 and be absorbed by the negative electrode electrolyte.

[0036] A vanadium redox flow battery consists of two reactive pairs, positive and negative. During charging, oxidation occurs at the positive electrode, and reduction occurs at the negative electrode.

[0037] Positive electrode reaction: VO 2+ +H₂O=e - +VO2 + +2H + (1V)

[0038] Negative electrode reaction: V 3+ +e - =V 2+ (-0.225V)

[0039] During the discharge process, a reduction reaction occurs at the positive electrode, and an oxidation reaction occurs at the negative electrode, which are the opposite of the reactions described above.

[0040] Theoretically, placing the same amount of active ions at the positive and negative electrodes of a battery allows it to achieve charge and discharge capabilities. Specifically, at the initial charging state, if the mass of tetravalent vanadium ions in the positive electrode electrolyte is equal to that of trivalent vanadium ions in the negative electrode electrolyte, the number of electrons that can be charged into both electrodes is the same. Similarly, at the initial discharging state, if the mass of pentavalent vanadium ions in the positive electrode is equal to that of divalent vanadium ions in the negative electrode, the number of electrons that can be released by the electrochemical reaction at both electrodes is the same. The battery's capacity depends on the minimum of these two values. Specifically, at the initial charging state, the lowest mass of tetravalent vanadium ions in the positive electrode electrolyte and trivalent vanadium ions in the negative electrode electrolyte determines the amount of chargeable battery; at the initial discharging state, the lowest mass of pentavalent vanadium ions in the positive electrode and divalent vanadium ions in the negative electrode determines the amount of dischargeable battery.

[0041] At the negative electrode of the battery, the reduction reaction of hydrogen readily occurs: 2H₂O + +2e - =H2; (0V)

[0042] The potential of divalent and trivalent vanadium at the negative electrode is lower than the standard potential for the hydrogen evolution reaction (HER). However, because carbon felt is used as the electrode in the battery, its HER overpotential is relatively high, thus largely suppressing the HER reaction. Nevertheless, the HER reaction cannot be completely suppressed, and it is irreversible. When the HER reaction occurs, the corresponding reaction at the positive electrode is vanadium oxidation. As the battery cycles through charge and discharge, the amount of HER gradually accumulates, and the total amount of tetravalent vanadium in the positive electrode electrolyte decreases, leading to a gradual reduction in the battery's rechargeability.

[0043] Understandably, in order to restore battery capacity, the system of this embodiment utilizes the reaction occurring in the positive electrode electrolyte within the positive electrode storage tank 10 to reduce the valence state of active ions and generate a first oxidizing gas. Specifically, this involves reducing pentavalent vanadium to tetravalent vanadium, increasing the total amount of tetravalent vanadium in the positive electrode, so that in the initial stage of charging, its mass is close to that of trivalent vanadium in the negative electrode, thereby restoring battery capacity. Referring to Figure 1, in some embodiments, the recovery system of this application is a self-circulating closed system. The entire process does not introduce any additional devices or gas sources, nor does it require the addition of external recovery agents, thus ensuring the restoration of battery capacity and reducing electrolyte contamination.

[0044] In some embodiments, referring to FIG1, the positive electrode storage tank 10 includes a first outlet 101 and a first inlet 102, and the catalytic reaction device 20 includes a second inlet 201 and a second outlet 202. The recovery system further includes a first pipeline 40 and a second pipeline 50. The first pipeline 40 is connected to the first outlet 101 and the second inlet 201, respectively, for conveying the first oxidizing gas from the positive electrode storage tank 10 to the catalytic reaction device 20. The second pipeline 50 is connected to the second outlet 202 and the first inlet 102, respectively, for conveying the remaining first oxidizing gas from the catalytic reaction device 20 back to the positive electrode storage tank 10 after catalyst oxidation. It can be understood that the arrangement of the first pipeline 40 and the second pipeline 50 realizes the cyclic delivery of the first oxidizing gas. The first oxidizing gas is conveyed from the positive electrode storage tank 10 to the catalytic reaction device 20 through the first pipeline 40, and then conveyed back to the positive electrode storage tank 10 through the second pipeline 50. This cyclic delivery ensures the full utilization of the gas. It can maintain the balance between active ions and reducing ions in the positive and negative electrode electrolytes, which helps to reduce the problem of high average valence state of the positive and negative electrode electrolytes caused by side reactions such as hydrogen evolution in traditional flow batteries, thereby mitigating the impact of battery capacity decay.

[0045] In some embodiments, referring to FIG1, the recovery system further includes a first one-way valve 401, which is disposed on the first pipeline 40. The first one-way valve 401 ensures that the first oxidizing gas can only flow out of the positive electrode storage tank 10 and cannot flow back into the positive electrode storage tank 10.

[0046] In some embodiments, referring to FIG2, the recovery system further includes a positive electrode recovery device 60, which is connected to the positive electrode storage tank 10. The positive electrode recovery device 60 can receive the positive electrode electrolyte and promote the reaction of the positive electrode electrolyte to generate a second oxidizing gas. The positive electrode recovery device 60 is also connected to a catalytic reaction device 20, which can receive the second oxidizing gas and is used to oxidize the catalyst.

[0047] It should be noted that the positive electrode recovery device 60 is a device that promotes the reaction of the positive electrode electrolyte, reduces the active materials in the positive electrode electrolyte, and generates a second oxidizing gas; the second oxidizing gas can be either chlorine or bromine. When the reaction rate between the reducing ions and high-valence active ions in the positive electrode electrolyte is too slow, or when it is necessary to significantly reduce the valence state of the active ions in the electrolyte, the positive electrode recovery device 60 needs to be connected; a high SOC positive electrode electrolyte is pumped into the positive electrode recovery device, and the temperature is controlled to achieve the redox reaction between the reducing ions and the active high-valence ions, generating a second oxidizing gas, thereby reducing the valence state of the active ions in the positive electrode electrolyte and achieving the purpose of restoring battery capacity.

[0048] In some embodiments, referring to FIG2, the positive electrode storage tank 10 includes a first outlet end 103 and a first inlet end 104, and the positive electrode recovery device 60 includes a second inlet end 601 and a second outlet end 602. The recovery system further includes a third pipeline 70 and a fourth pipeline 80. The third pipeline 70 is connected to the first outlet end 103 and the second inlet end 601 respectively, and is used to transport the positive electrode electrolyte from the positive electrode storage tank 10 to the positive electrode recovery device 60. The fourth pipeline 80 is connected to the second outlet end 602 and the first inlet end 104 respectively, and is used to transport the reacted positive electrode electrolyte back to the positive electrode storage tank 10. It can be understood that the third pipeline 70 and the fourth pipeline 80 are used to pump the high SOC positive electrode electrolyte out of the positive electrode storage tank 10 and introduce it into the positive electrode recovery device 60 for reaction recovery, and then return it to the positive electrode storage tank 10.

[0049] In some embodiments, referring to FIG2, the positive electrode recovery device 60 further includes a third outlet 603 and a third inlet 604; the recovery system further includes a fifth pipeline 90 and a sixth pipeline 100. The fifth pipeline 90 is connected to the third outlet 603 and the second inlet 201, respectively, for conveying the second oxidizing gas from the positive electrode recovery device 60 to the catalytic reaction device 20; the sixth pipeline 100 is connected to the second outlet 202 and the third inlet 604, respectively, for conveying the remaining second oxidizing gas from the catalytic reaction device 20 back to the positive electrode recovery device 60 after catalyst oxidation. The arrangement of the fifth pipeline 90 and the sixth pipeline 100 can maintain the balance of active ions and reducing ions in the positive and negative electrode electrolytes, which helps to reduce the problem of high average valence state of the positive and negative electrode electrolytes caused by side reactions such as hydrogen evolution in traditional flow batteries, thereby mitigating the impact of battery capacity decay.

[0050] In some embodiments, referring to FIG2, the recovery system further includes a second one-way valve 901, which is disposed on the fifth pipeline 90. The second one-way valve 901 allows the first oxidizing gas to flow out of the positive electrode recovery device 60 and prevents the first reducing gas from flowing into the positive electrode recovery device 60.

[0051] In some embodiments, referring to Figure 1, the negative electrode storage tank 30 includes a fourth gas outlet 301 and a fourth gas inlet 302. The recovery system further includes a seventh pipeline 200 and an eighth pipeline 300. The seventh pipeline 200 is connected to the fourth gas outlet 301 and the second gas inlet 201, respectively, for conveying the first reducing gas from the negative electrode storage tank 30 to the catalytic reaction device 20. The eighth pipeline 300 is connected to the second gas outlet 202 and the fourth gas inlet 302, respectively, for conveying the gas generated after oxidation by the catalyst in the catalytic reaction device 20 back to the negative electrode storage tank 30. It should be noted that the seventh pipeline 200 and the eighth pipeline 300 realize the circulation of the first reducing gas and the gas generated after oxidation by the catalyst in the catalytic reaction device 20.

[0052] In some embodiments, the recovery system further includes a third one-way valve 2001, which is disposed on the seventh pipeline 200. The third one-way valve 2001 allows the first reducing gas to flow out of the negative electrode storage tank 30 and prevents the first oxidizing gas and the second oxidizing gas from flowing into the negative electrode storage tank 30.

[0053] In some embodiments, referring to FIG3, the recovery system further includes: a reducing gas source 400 and a tail gas treatment device 500. The reducing gas source 400 is connected to the catalytic reaction device 20 and is used to introduce a second reducing gas into the catalytic reaction device 20. The catalytic reaction device 20 receives the second reducing gas, and the second reducing gas is used to reduce the oxidized catalyst. The tail gas treatment device 500 is connected to the negative electrode storage tank 30 and is used to treat the gas discharged from the negative electrode storage tank 30. It is understood that the setting of the reducing gas source 400 can provide the second reducing gas to the catalytic reaction device 20, which can ensure that the catalyst in the catalytic reaction device 20 is completely reduced, maximizing the reaction amount of the catalyst with the first oxidizing gas and the second oxidizing gas. The tail gas treatment device 500 can ensure that the gas discharged from the negative electrode storage tank 30 is discharged after producing water or carbon dioxide through catalytic oxidation, reducing environmental pollution.

[0054] In some embodiments, the catalyst is selected from at least one of copper-based catalysts, nickel-based catalysts, and bismuth-based catalysts. Copper-based catalysts include, but are not limited to, copper, copper oxide, copper chloride, cuprous chloride, copper bromide, copper iodide, and copper-containing alloys; nickel-based catalysts include, but are not limited to, nickel, nickel oxide, nickel chloride, nickel bromide, and nickel-containing alloys; bismuth-based catalysts include, but are not limited to, bismuth, bismuth oxide, bismuth chloride, bismuth bromide, and bismuth-containing alloys.

[0055] In some embodiments, the reduced state of the catalyst can be determined by its color appearance, such as a metallic luster. Referring to Figure 6, the catalyst is light-colored before oxidation, dark-colored after oxidation, and returns to a light-colored state after reduction.

[0056] In some embodiments, the reducing ion is selected from at least one of chloride ions and bromide ions.

[0057] In some embodiments, the reducing ions are provided by a component that releases chloride or bromide ions, such as one or a mixture of perchloric acid, hypochlorous acid, chloric acid, hydrochloric acid, liquid bromine, hypobromic acid, hydrobromic acid, and bromic acid.

[0058] In some embodiments, the active ion is selected from at least one of vanadium ion, manganese ion, bromide ion, iron ion, and lead ion.

[0059] In some embodiments, the negative electrode electrolyte contains one or a mixture of several of the following: vanadium ions, chromium ions, manganese ions, titanium ions, iron ions, zinc ions, tin ions, bismuth ions, and mercury ions.

[0060] In some embodiments, the supporting electrolyte is selected from at least one of sulfuric acid, hydrochloric acid, and phosphoric acid.

[0061] In some embodiments, the first oxidizing gas is selected from at least one of chlorine and bromine.

[0062] In some embodiments, the first reducing gas is hydrogen.

[0063] In some embodiments, the second oxidizing gas is selected from at least one of chlorine and bromine.

[0064] In some embodiments, the second reducing gas is selected from at least one of hydrogen, carbon monoxide, methane, and propane.

[0065] In some embodiments, the SOC of the positive electrode electrolyte before the reaction is 60% to 100%, and the SOC of the positive electrode electrolyte after the reaction is 50% to 100%. Optionally, the SOC of the positive electrode electrolyte before the reaction is 75% to 90%, and the SOC of the positive electrode electrolyte after the reaction is 60% to 70%. Here, SOC (State of Charge) represents the state of charge of the battery, which indicates the ratio between the amount of charge currently stored in the battery and its maximum charge capacity.

[0066] In some embodiments, referring to Figure 5, a flow battery cycle recovery method is also provided, including the following steps:

[0067] A positive electrode electrolyte is introduced into the positive electrode storage tank 10. The positive electrode electrolyte contains reducing ions and active ions. The reducing ions react with the active ions to reduce the valence state of the active ions and generate the first oxidizing gas.

[0068] The first oxidizing gas is introduced into the catalytic reaction device 20, which contains a catalyst. The first oxidizing gas reacts with the catalyst to oxidize the catalyst.

[0069] A negative electrode electrolyte is introduced into the negative electrode storage tank 30. The negative electrode electrolyte contains a supporting electrolyte. The supporting electrolyte is prone to side reactions during battery charging or in the charging state to produce the first reducing gas.

[0070] The first reducing gas is introduced into the catalytic reaction device 20. The first reducing gas reacts with the oxidized catalyst to undergo an oxidation-reduction reaction. The catalyst is reduced and releases acidic gas. The generated acidic gas can return to the negative electrode storage tank 30 and be absorbed by the negative electrode electrolyte.

[0071] Understandably, the method in this application links the recovery process with the amount of battery capacity decay and SOC, thereby achieving automatic battery recovery. The flow battery cycle recovery system solves the problem of battery capacity decay caused by the high average valence state of the positive and negative electrode electrolytes due to side reactions such as hydrogen evolution in flow batteries.

[0072] In some embodiments, the molar ratio of reducing ions to active ions is in the range of 1 to 10 to 0.1 to 5. Optionally, the molar ratio of reducing ions to active ions can be any one of 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, or a range between any two of these ratios.

[0073] In some embodiments, the concentration of reducing ions in the positive electrode electrolyte is from 0.5 mol / L to 10 mol / L; for example, it can be any one or a range between any two of the following values: 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, 6 mol / L, 7 mol / L, 8 mol / L, 9 mol / L, and 10 mol / L.

[0074] In some embodiments, the concentration of active ions in the positive electrode electrolyte is from 0.1 mol / L to 5 mol / L. For example, it can be any one or a range between any two of the following values: 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, and 5 mol / L.

[0075] In some embodiments, the concentration of the electrolyte in the negative electrode electrolyte is supported to be from 0.5 mol / L to 10 mol / L. For example, it can be any one value or a range between any two values ​​from 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, 6 mol / L, 7 mol / L, 8 mol / L, 9 mol / L, and 10 mol / L.

[0076] In some embodiments, the temperature at which the reducing ions react with the active ions is between 20°C and 100°C. For example, it can be any one or a range between any two of the following values: 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, and 100°C.

[0077] In some embodiments, the temperature at which the first oxidizing gas reacts with the catalyst is from 20°C to 400°C; for example, it can be any one or a range between any two of the following values: 20°C, 50°C, 100°C, 120°C, 150°C, 180°C, 200°C, 250°C, 300°C, 350°C, and 400°C.

[0078] In some embodiments, the reaction temperature of the first reducing gas with the oxidized catalyst is 100°C to 550°C; for example, it can be any one or a range between any two of 100°C, 150°C, 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, 500°C, and 550°C.

[0079] In some embodiments, prior to the step of reacting the reducing ion with the active ion, the method further includes:

[0080] The positive electrode electrolyte is introduced into the positive electrode recovery device 60. By adjusting the temperature, the positive electrode electrolyte reacts to produce a second oxidizing gas and reduces the valence state of the active ions.

[0081] The second oxidizing gas is introduced into the catalytic reaction device 20, where it reacts with the catalyst to oxidize it.

[0082] Understandably, the positive electrode recovery device 60 can further enhance the reaction between reducing ions and active ions in the positive electrode electrolyte to ensure the generation of a second oxidizing gas, thereby reducing the valence state of active ions in the positive electrode electrolyte and achieving the purpose of restoring battery capacity. The second oxidizing gas and the first oxidizing gas are the same gas, which can be used for the reaction with the catalyst to generate oxidation.

[0083] In some embodiments, the temperature range in the positive electrode recovery device 60 is 20°C to 100°C. For example, the temperature can be any one or a range between any two of the following values: 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, and 100°C.

[0084] In some embodiments, this occurs before the step of reacting the first oxidizing gas with the catalyst and / or after the step of reacting the first reducing gas with the already oxidized catalyst. When the amount of the first reducing gas is insufficient, the catalyst cannot be completely reduced.

[0085] The second reducing gas provided by the reducing gas source 400 is introduced into the catalytic reaction device 20 to completely reduce the catalyst;

[0086] The gas produced after the reaction is introduced into the negative electrode storage tank 30, and then treated by the tail gas treatment device 500 before being discharged.

[0087] Understandably, in addition to the flow battery cycle recovery system, an optional external reducing gas source 400 recovery system is provided, which can make external intervention adjustments to the electrolyte according to the actual operating conditions.

[0088] Using the above-mentioned flow battery cycle recovery method, the battery's charge and discharge cycle capacity shows almost no decay, truly achieving the characteristics of a long-life, non-degrading flow battery.

[0089] Specifically, a method for restoring a flow battery is provided, including:

[0090] Step 1: Load the catalyst into the catalytic reaction device 20, circulate the catalytic reaction device 20 to the reducing gas source 400, and introduce the second reducing gas into the catalyst placed in the catalytic reaction device 20 for pre-reduction; taking nickel oxide as an example, the following reaction occurs: NiO(s) + CO(g) = Ni(s) + CO2(g);

[0091] The gas produced after the reaction is introduced into the negative electrode storage tank through the external circulation pipeline, and then discharged after passing through the tail gas treatment device 500; after the reaction is completed, it proceeds to step 2; if a reducing catalyst is used, it proceeds directly to step 2.

[0092] Step 2: Under high SOC conditions, reducing ions react with high-valence active ions in the positive electrode storage tank 10 to produce the first oxidizing gas, as shown in the following reaction:

[0093] Step 3: Switch the internal circulation pipeline and pump the first oxidizing gas into the catalytic reaction device 20 through the first pipeline 40. Taking nickel catalyst as an example, the catalytic reaction device 20 undergoes an absorption reaction to generate nickel chloride; the residual gas returns to the positive electrode storage tank 10 through the second pipeline 50 to achieve cyclic absorption.

[0094] Step 4: Switch the circulation pipeline and pump the first reducing gas generated in the negative electrode storage tank 30 into the catalytic reaction device 20 through the seventh pipeline 200 to reduce the catalyst; taking nickel chloride as an example, the reaction that occurs is as follows: NiCl2(s)+H2(g)=Ni(s)+2HCl(g);

[0095] The gas (hydrogen chloride) generated in the catalytic reaction device 20 is introduced into the negative electrode storage tank 30 through the eighth pipeline 300; within a certain circulation volume, the catalyst is reduced to the target state, and the process returns to step 2 to achieve internal circulation; otherwise, it proceeds to step 5.

[0096] Step 5: Switch the circulation pipeline and introduce external reducing gas (H2) to reduce the catalyst. The reaction is the same as in Step 4. When the catalyst is reduced to the target state, return to Step 2.

[0097] Step 6: When the reaction rate between the reducing ions and high-valence active ions in the positive electrode electrolyte is too slow or when it is necessary to significantly reduce the valence state of active ions in the positive electrode electrolyte, connect the positive electrode recovery device 60; pump the high SOC positive electrode electrolyte into the positive electrode recovery device 60 through the third pipeline 70, and adjust the temperature to achieve the redox reaction between the reducing ions and the active high-valence ions, generating halogen gas (such as chlorine gas), thereby reducing the valence state of active ions in the positive electrode electrolyte and achieving the purpose of restoring battery capacity. The reaction is the same as in step 2; then the reacted positive electrode electrolyte is transported back to the positive electrode storage tank 10 through the fourth pipeline 80.

[0098] Step 7: Pump the gas (including halogen gas) in the positive electrode recovery device 60 into the catalytic reaction device 20 through the fifth pipeline 90, and the reaction is the same as in step 3; the residual gas is pumped into the positive electrode recovery device 60 through the sixth pipeline 100 to achieve cyclic absorption; then proceed to step 4 or step 5 again.

[0099] In the above recovery method, the liquid circulation mode for positive electrode electrolyte recovery is: positive electrode storage tank - positive electrode recovery device - positive electrode storage tank.

[0100] In the above recovery methods, the circulation mode of the gas oxidation catalyst includes: 1) positive electrode storage tank - catalytic reaction device - positive electrode storage tank; 2) positive electrode recovery device - catalytic reaction device - positive electrode recovery device;

[0101] In the above-mentioned recovery method, the circulation mode of the gas reduction catalyst includes: 1) negative electrode storage tank - gas device - negative electrode storage tank; 2) reducing gas source - catalytic reaction device - negative electrode storage tank - tail gas treatment device.

[0102] Specific applications

[0103] Referring to Table 1, the initial average valence state of vanadium ions in the positive and negative electrode electrolytes of the flow battery was 3.503. The single-sided capacity of the positive and negative electrode electrolytes was 15894.83 Ah for the positive electrode and 15964.52 Ah for the negative electrode, respectively. The theoretical maximum capacity of the battery was 15894.83 Ah. The initial concentration of pentavalent vanadium in the positive electrode was 0.069 mol / L. After 100 charge-discharge cycles, the average valence state of vanadium ions in the positive and negative electrodes increased from the initial 3.503 to 3.601. The single-sided capacity of the positive and negative electrode electrolytes was 14054.07 Ah for the positive electrode and 16800.69 Ah for the negative electrode, respectively. The theoretical maximum capacity of the battery decreased to 14054.07 Ah. After 100 cycles, the flow battery is charged to a high SOC state. The valence state is adjusted using the flow battery cycle recovery system provided in this application embodiment. The temperature of the catalytic reaction device is adjusted to 100°C, and chlorine gas is circulated into the positive electrode storage tank until the catalyst surface turns blackish-gray. Then, the temperature of the catalytic reaction device is adjusted to 450°C, and hydrogen gas generated by the hydrogen evolution reaction in the negative electrode storage tank is circulated for 60 minutes. Then, the external reducing gas is switched until the catalyst color turns silver-gray.

[0104] Table 1

[0105] The results of the segmented sampling and testing are shown in Table 1. After the first recovery cycle, the positive electrode SOC decreased from 88.81% to 73.17%, the average valence state of vanadium ions recovered to 3.495, and the theoretical maximum capacity recovered to 16119.37 Ah. Three more charge-discharge cycles were performed, and the results showed that the theoretical maximum capacity recovered to 15964.52 Ah. Therefore, the recovery system described in this application can effectively maintain battery capacity.

[0106] The above provides a detailed description of a flow battery cycle recovery system and recovery method provided in the embodiments of this application. Specific examples have been used in this application to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the technical solutions and core ideas of this application. Those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A flow battery cycle recovery system, comprising: A positive electrode storage tank is provided, which contains a positive electrode electrolyte containing reducing ions and active ions. The reducing ions can react with the active ions to reduce the valence state of the active ions and generate a first oxidizing gas. A catalytic reaction device, wherein the catalytic reaction device contains a catalyst, the catalytic reaction device is connected to the positive electrode storage tank, the catalytic reaction device is capable of receiving the first oxidizing gas, and the first oxidizing gas is configured to oxidize and fix the catalyst; A negative electrode storage tank is provided, which contains a negative electrode electrolyte containing a supporting electrolyte. The supporting electrolyte undergoes a side reaction to generate a first reducing gas. The negative electrode storage tank is connected to a catalytic reaction device, which is also capable of receiving the first reducing gas. The first reducing gas is configured to reduce the oxidized catalyst. The generated acidic gas can be returned to the negative electrode storage tank and absorbed by the negative electrode electrolyte. The positive electrode storage tank includes a first gas outlet and a first gas inlet, and the catalytic reaction device includes a second gas inlet and a second gas outlet. The flow battery cycle recovery system also includes: A first pipeline is connected to the first outlet and the second inlet respectively, and is configured to transport the first oxidizing gas from the positive electrode storage tank to the catalytic reaction device. The second pipeline is connected to the second gas outlet and the first gas inlet respectively, and is configured to transport the remaining first oxidizing gas back to the positive electrode storage tank by the catalytic reaction device after the catalyst oxidation.

2. The liquid flow battery cycle recovery system of claim 1, wherein, The flow battery cycle recovery system also includes: The first one-way valve is located on the first pipeline.

3. The liquid flow battery cycle recovery system of claim 1, wherein, The flow battery cycle recovery system also includes: A positive electrode recovery device is connected to the positive electrode storage tank. The positive electrode recovery device can receive the positive electrode electrolyte and promote the reaction of the positive electrode electrolyte to generate a second oxidizing gas. The positive electrode recovery device is also connected to the catalytic reaction device, which is capable of receiving the second oxidizing gas, and the second oxidizing gas is configured to oxidize and fix the catalyst.

4. The liquid flow battery cycle recovery system of claim 3, wherein, The positive electrode storage tank includes a first outlet and a first inlet, the positive electrode recovery device includes a second inlet and a second outlet, and the flow battery cycle recovery system further includes: The third pipeline is connected to the first liquid outlet and the second liquid inlet respectively, and is configured to transport the positive electrode electrolyte from the positive electrode storage tank to the positive electrode recovery device. The fourth pipeline is connected to the second liquid outlet and the first liquid inlet respectively, and is configured to transport the reacted positive electrolyte back to the positive electrolyte storage tank.

5. The liquid flow battery cycle recovery system of claim 4, wherein, The positive electrode recovery device further includes a third air outlet and a third air inlet; the flow battery cycle recovery system further includes: The fifth pipeline is connected to the third outlet and the second inlet respectively, and is configured to transport the second oxidizing gas from the positive electrode recovery device to the catalytic reaction device; The sixth pipeline is connected to the second outlet and the third inlet respectively, and is configured to transport the remaining second oxidized gas from the catalytic reaction device back to the positive electrode recovery device after the catalyst oxidation.

6. The liquid flow battery cycle recovery system of claim 5, wherein, The flow battery cycle recovery system also includes: The second one-way valve is located on the fifth pipeline.

7. The liquid flow battery cycle recovery system of claim 3, wherein, The negative electrode storage tank includes a fourth air outlet and a fourth air inlet, and the flow battery cycle recovery system further includes: The seventh pipeline is connected to the fourth outlet and the second inlet respectively, and is configured to transport the first reducing gas from the negative electrode storage tank to the catalytic reaction device. The eighth pipeline is connected to the second gas outlet and the fourth gas inlet respectively, and is configured to transport the gas generated by the catalyst oxidation in the catalytic reaction device back to the negative electrode storage tank.

8. The liquid flow battery cycle recovery system of claim 7, wherein, The flow battery cycle recovery system also includes: The third one-way valve is located on the seventh pipeline.

9. The liquid flow battery cycle recovery system of claim 7, wherein, The flow battery cycle recovery system also includes: A reducing gas source is connected to the catalytic reaction device and configured to introduce a second reducing gas into the catalytic reaction device; the catalytic reaction device receives the second reducing gas, and the second reducing gas is configured to reduce the oxidized catalyst. An exhaust gas treatment device is connected to the negative electrode storage tank and configured to treat the gas discharged from the negative electrode storage tank.

10. The liquid flow battery cycle recovery system of claim 1, wherein, The flow battery cycle recovery system satisfies at least one of the following conditions: The catalyst is selected from at least one of copper-based catalysts, nickel-based catalysts, and bismuth-based catalysts; The reducing ion is selected from at least one of chloride ion and bromide ion; The active ion is selected from at least one of vanadium ion, manganese ion, bromide ion, iron ion, and lead ion; The supporting electrolyte is selected from at least one of sulfuric acid, hydrochloric acid, and phosphoric acid; The first oxidizing gas is selected from at least one of chlorine and bromine; The first reducing gas is hydrogen.

11. The liquid flow battery cycle recovery system of claim 9, wherein, The flow battery cycle recovery system satisfies at least one of the following conditions: The second oxidizing gas is selected from at least one of chlorine and bromine; The second reducing gas is selected from at least one of hydrogen, carbon monoxide, methane, and propane.

12. The liquid flow battery cycle recovery system of claim 3, wherein, The positive electrode electrolyte has a state of charge (SOC) of 60% to 100% before the reaction; The positive electrode electrolyte has a state of charge (SOC) of 50% to 100% after the reaction.

13. A method for cycling and restoring a flow battery, comprising the following steps: The positive electrode storage tank contains a positive electrode electrolyte containing reducing ions and active ions. The reducing ions react with the active ions to reduce the valence state of the active ions and generate a first oxidizing gas. The first oxidizing gas is introduced into a catalytic reaction device containing a catalyst, and the first oxidizing gas undergoes an oxidation-reduction reaction with the catalyst and is fixed. The negative electrode storage tank contains a negative electrode electrolyte, which contains a supporting electrolyte, and the supporting electrolyte undergoes a side reaction to produce a first reducing gas. The first reducing gas is introduced into the catalytic reaction device, where it undergoes an oxidation-reduction reaction with the oxidized catalyst. The catalyst is reduced and releases acidic gas, which is then returned to the negative electrode storage tank and absorbed by the negative electrode electrolyte.

14. The flow battery cycle recovery method of claim 13, wherein, The molar ratio of the reducing ion to the active ion is in the range of 1 to 10 to 0.1 to 5. The concentration of the reducing ions in the positive electrode electrolyte is from 0.5 mol / L to 10 mol / L; The concentration of the active ions in the positive electrode electrolyte is from 0.1 mol / L to 5 mol / L; The concentration of the supporting electrolyte in the negative electrode electrolyte is from 0.5 mol / L to 10 mol / L.

15. The flow battery cycle recovery method of claim 13, wherein, The flow battery cycle recovery method satisfies at least one of the following conditions: The temperature at which the reducing ions react with the active ions is between 20°C and 100°C. The reaction temperature between the first oxidizing gas and the catalyst is from 20°C to 400°C; The reaction temperature between the first reducing gas and the already oxidized catalyst is between 100°C and 550°C.

16. The flow battery cycle recovery method of claim 13, wherein, Prior to the step of the reaction between the reducing ions and the active ions, the flow battery cycle recovery method further includes: The positive electrode electrolyte is introduced into the positive electrode recovery device. By adjusting the temperature, the positive electrode electrolyte reacts to produce a second oxidizing gas and reduces the valence state of the active ions. A second oxidizing gas is introduced into the catalytic reaction device, where it reacts with the catalyst to oxidize it.

17. The flow battery cycle recovery method of claim 13, wherein, In the positive electrode recovery device, the temperature range is 20°C to 100°C.

18. The flow battery cycle recovery method of claim 13, wherein, The flow battery cycle recovery method further includes, before the step of reacting the first oxidizing gas with the catalyst and / or after the step of reacting the first reducing gas with the already oxidized catalyst: A second reducing gas supplied by a reducing gas source is introduced into a catalytic reaction device, and the first reducing gas reacts with at least a portion of the catalyst that has been oxidized to completely reduce the catalyst. The gas produced after the reaction is introduced into the negative electrode storage tank and absorbed by the negative electrode electrolyte; then it is treated by the exhaust gas treatment device and discharged.

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